Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP LTE systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
MIMO systems employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels or carriers. Each of the NS independent channels corresponds to a dimension. These multicarrier systems can provide improved performance if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. For example, each device can be provided with two or more carrier frequencies on which to transmit information, which can lead to higher throughput and/or greater reliability.
Such multicarrier systems, however, present significant technical challenges beyond their single carrier predecessors. One such challenge is managing the number of carriers used to transmit data. In general, using more carriers leads to better performance, e.g., a higher throughput. However, there is a limited amount of transmit power and each carrier has its own power requirements based on overhead and channel characteristics. It may be more efficient to only transmit on a subset of the carriers, or in some instances to drop assigned carriers when their overhead requirements become too burdensome. Accordingly, managing multiple carriers is not a simple extension of single carrier concepts to a multicarrier system.